Introduction to Channels

In this lesson, explore introduction to channels through one small Go program, and connect its output to the language rules behind it.

A channel is a typed communication path between goroutines. A send uses ch <- value, and a receive uses value := <-ch.

Channel operations also provide synchronization. Channels are especially useful when one goroutine owns the task of producing data and another consumes it.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func main() {
	messages := make(chan string)
	go func() { messages <- "ready" }()
	message := <-messages
	fmt.Println("Message:", message)
}

Output

Message: ready

The unbuffered send waits until the receiver is available. The receive transfers ready and the program prints Message: ready.

• A channel’s element type is fixed.
• Closing a channel is not required simply because its last send finished.

Change the channel to carry an int, send 42, and print the received value.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Introduction to Channels in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.